1. Field of the Invention
The present invention relates to a process for producing an aluminum alloy having a high strength high hardness, and high heat resistance which warrant its use in many industrial fields including automobiles, aircrafts and electric machines and equipment.
2. Description of the Related Art
There is a great demand for high-strength aluminum alloys with high specific strength in the fields of automobiles, aircrafts, and office equipment, because they are expected to exhibit high performance when used for rapid moving parts. For this reason, many attempts have been made to produce them by rapid cooling or mechanical alloying. In fact, rapid cooling has realized an amorphous material (in the form of 0.02 mm thick ribbon) having a tensile strength in excess of 100 kgf/mm.sup.2 by melt spinning from a molten alloy of aluminum, a transition metal (e.g., Fe, Co, and Ni), and a rare earth element (e.g. , Y, La, and Ce) . (See Nippon Kinzoku Gakkaishi, vol. 30, No. 5, 1991, p.375.) Rapid cooling has also realized a material (in the form of mass) having a tensile strength of 100 kgf/mm .sup.2 by extrusion at above the phase transformation temperature from an amorphous powder produced by rapidly solidifying an alloy of aluminum and a transition metal (Japanese Patent Laid-Open No. 202431/1991).
On the other hand, mechanical alloying is used to form an amorphous phase from an aluminum powder mixed with a powder of titanium, nickel, niobium, or zirconium in a widely varied ratio by mechanical mixing, grinding, and aggregation which are combined together. (No data is available on the strength of material in the form of mass produced by mechanical alloying.) Mechanical alloying has been used to finely disperse iron particles into aluminum. The resulting material has a tensile strength higher than 55 kgf/mm.sup.2 after rolling.
The aluminum alloy obtained by mechanical alloying is available usually in the form of powder having a particle diameter of several micrometers to tens of micrometers. The aluminum alloy obtained by rapid cooling is available in the form of ribbon having a thickness of about 20 .mu.m. However, it is expensive because it contains a large amount of expensive rare earth elements. Aluminum alloys in the form of powder or ribbon are limited in application areas. If an aluminum alloy in the form of amorphous powder is to be made into practical parts, the powder needs consolidation. The consolidation may be accomplished by hot isostatic pressing (HIP) or canning extrusion at 400.degree.-550.degree. in a non-oxidizing atmosphere. The consolidation by these processes involving heating crystallizes the amorphous phase and hence gives rise to an alloy of crystalline structure. Canning extrusion at low temperatures yields an alloy of poor strength due to incomplete bonding between powder particles. In other words, the above-mentioned conventional processes, such as rapid cooling and mechanical alloying, yield an amorphous material in the form of powder or ribbon which has to be processed afterwards into desired products by canning extrusion or the like. For this reason there is a strong demand for an economical and easy process for producing a high-strength amorphous aluminum alloy in the form of mass.